The present invention relates to a flame detection and proof control device for detecting flame in a gas-fired system. It finds particular utility in use with a regulated sealed combustion heating system, but can be used in a wide variety of systems and appliances which require safety controls.
It is important for reasons of safety that gas appliances be equipped with a flame detection and control unit which will assure shut-off of gas when no flame is present. The control must also allow for a period for ignition when the gas is on even though there is no flame. When the gas has not been ignited, the system must operate to quickly close the gas valve.
There are a number of types of gas appliances, including heating and air conditioning systems, stoves, dryers, etc., for which such a flame detection and proof device is required. For many years, gas appliances have operated with a pilot light system which ignites the main gas jet when the appliance is turned on. However, in recent years it has been recognized that such systems are not fuel or energy efficient. Consequently, other systems have been introduced to replace the pilot light type of system.
Spark ignition systems have also been used which, in effect, ignite the gas by creating a spark across an ignition gap. These systems are more energy efficient than the pilot light type system, but have not been found to operate well with the regulated sealed combustion heating system.
In recent years flame igniters, usually comprised of silicon carbide, have been developed which can be heated rapidly by applying an AC voltage thereto. The igniters have provided an efficient way of providing ignition of the gas.
Control devices for the above types of ignition systems which have been used in the prior art with gas-fired systems have had certain disadvantages. Relatively high voltage power sources of the order of 220 volts have been required to operate the prior art safety controls. Also, such systems have not always given 100 percent protection in assuring that gas will be shut off if ignition is not effected.